利用TEM, SEM及物理化学相分析法, 研究了回火温度对高Ti微合金直接淬火高强钢显微组织和力学性能的影响. 结果表明, 随着回火温度的升高, 抗拉曲线出现明显的转折点, 抗拉强度先降低后升高, 而屈服强度缓慢升高. 回火温度为600 ℃时, 实验钢具有最佳的综合力学性能; 抗拉强度为1043 MPa, 屈服强度为1020 MPa, 延伸率为16%, -40 ℃冲击功为67.7 J. 其主要原因是600 ℃时, 纳米级的析出相数量最多, 体积分数最大, 分布最均匀. 600 ℃回火时, 实验钢的固溶强化和沉淀强化的强度增量分别约为149.82 和171.72 MPa.

Over the past years, Ti microalloying technique has not been developed sufficiently compared to Nb and V, due to its special metallurgy characteristics. Higher chemical activity of Ti results in larger inclusions when Ti combines with O, N and S. In addition, higher temperature sensitivity of TiC precipitation leads to the instability of steel strips. Owning to the above reasons, the conventional high strength steels with the microstructure of martensite, bainite or the composite of the two were microalloyed with (0.01%~0.03%)Ti (mass fraction) for austenite grain refinement during soaking. The addition of high Ti (>0.1%) in microalloyed high strength martensitic or bainitic steels were rarely touched upon. The effects of tempering temperature on the microstructure and mechanical properties of high Ti microalloyed directly quenched high strength steel were investigated by TEM, SEM and physical-chemical phase analysis. The results show that with the increase of tempering temperature, the tensile curve has an obvious turning point. The tensile strength gradually decreases first and then increases, while the yield strength increases slowly. At tempering temperature 600 ℃, the experimental steel shows the best mechanical properties with tensile strength at 1043 MPa, yield strength at 1020 MPa and the elongation of 16%, while the Charpy impact energy is 67.7 J at -40 ℃. The main reason is that the amount of nanometer precipitates reaches the maximum, their distributions are also relatively uniform and the size is significantly small. The solid solution strengthening and precipitation strengthening increment of the experiment steel tempering at 600 ℃ were about 149.82 and 171.72 MPa, respectively.